France: PhD Opportunity in NDT/microsystems

THESIS TOPIC:
Nonlinear elastic imaging for MEMS reliability assessment

Description of the recruiting organization:
The “Institut d’Electronique, de Microlectronique et de Nanotechnologies” (IEMN UMR CNRS 8520) was
created in 1992. The IEMN has now more than 500 people working in fundamental science as well as
applied research in the fields of micro- and nano-technology, micro- and nano-electronics, microwave components and devices, opto-electronics, acoustics, telecommunications, and micro-systems. The technological facilities of the IEMN are composed of 1600 m2 of cleanrooms housing high level equipment for manufacturing of state-of-the-art components and devices, and many characterization facilities in nanoscience, nanotechnology, micro-electronics and Micro-Electro-Mechanical Systems (MEMS).
The LEMAC team at the IEMN is a new European Laboratory of Nonlinear Magneto-Acoustics,
created in December 2004 with the aim of development of new ultrasonic imaging systems and new types of micro-systems using innovative magnetic materials. In the field of ultrasonic imaging, the LEMAC is a leader in a new research area called “Non-linear imaging by Magneto-Acoustic Wave Phase Conjugation” (MAWPC). This technique combines the advantages of the wave phase conjugation (time reversal) with the principles of non-linear acoustics. The LEMAC/IEMN has also a great experience in elaboration and fabrication of MEMS: magnetostatic microvalves for active flow control, MEMS-based magnetostatic tactile interfaces, and MEMS reconfigurable radio frequency antennas. In short, the research institute is ideally equipped with facilities that enable the realization of the
current project.

Subject of the thesis
The present proposal is dedicated to the use of new nonlinear acoustic imaging techniques for nondestructive testing of MEMS reliability. The method is essentially based of the time reversal principle that enables, via producing waves with inverted wave fronts, to re-focus acoustical energy exactly at the acoustical sources, even in inhomogeneous media. Correspondingly, the nonlinear version of the method focuses wave harmonics on nonlinear sources i.e. on defects (cracks, delaminations, etc.) To produce waves with inverted wave fronts, the MAWPC technique that uses electromagnetic pumping of active magnetic materials is elaborated in our laboratory. Being applied to surface or guided acoustic waves, it represents an integrated method for in situ defect detection.
The project is funded by the French National Agency for Research (ANR “blanche” ANL-MEMS) for the period of 3 years.
The hired student will contribute to
1) the experimental development and validation of the MAWPC technique for localization and imaging
of defects in MEMS: fabrication and tests of active magnetic films of different materials,
manufacturing of representative samples with nanoscale defects, realization of the time reversal
experiment, producing images of real cracks in MEMS;
2) the numerical support of the study: application of the 3D Discontinuous Galerkin Finite Element
Method to propagation of ultrasound in structures containing cracks.

Candidate profile
An ideal candidate has to be autonomous in working on at least one of the two tasks. The applicant should have a strong background in acoustical experimentation and/or good numerical skills. Knowledge of nonlinear acoustics or contact mechanics will be appreciated.